Advances in the selective separation of matter have resulted in numerous developments in a wide variety of industries. Attention first centered on the science of membranology, beginning in about 1960, when integrally-skinned cellulose acetate hyperfiltration membranes were developed for hyperfiltration desalination of salt water. Developments followed in the areas of hemodialysis, electrodialysis, reverse osmosis, ultrafiltration, cell harvesting, membrane bioreactors, microfiltration, gas separation, controlled time release, gel permeation chromatography, hollow fiber technology, non-cellulosic polymer membranes, ionomer membranes, copolymer membranes, crosslinkable thermoplastic polymer membranes, emulsion-type liquid membranes and others. These innovations have gained general acceptance, and separation materials form the above disciplines are in widespread use in medical processes, pharmaceutical research and production, industrial processes, research tools and consumer products including consumer products packaging materials.
Controlled release of pharmaceuticals is now possible due to various technologies, which include application of slow-dissolving coatings to oral dosage form drugs. U.S. Pat. No. 4,755,180 discloses an oral drug dosage form in which an erodible material, formed as a film around the drug during manufacture, is eroded or leached from the wall of the dosage form, such erosion or leaching enabling controlled release of pharmaceutically active agents to the gastrointestinal environment. The erodible materials disclosed in U.S. Pat. No. 4,755,180 are typical of the polysaccharide (sugar) coatings common in such applications: poly(glycolic) or poly(lactic) acid compositions, gelatinous compositions, or leachable polysaccharides, salts or oxides. Enteric coatings are also known in the art, which do not dissolve in the stomach but allow enteric delivery of an orally dosed drug.
Although means are known for moving ions or molecules--or solvents--at simple rates, such as the "zero-order" or "first-order" release kinetics typical in controlled release pharmaceuticals, no technology has heretofore provided a noningestible means for complex separation technology in which the separation kinetics may change over time, in response to an environmental stimulus, in a pre-planned or pre-programmed manner; moving components into and out of a container to provide a better environment for the retained materials; or release of cells in a controlled manner. Accordingly, a need remains for a separation barrier which can provide complex separation protocols for particular separation applications entirely different from the oral pharmaceutical dosage forms.